1. Field of the Invention
This invention relates to improvements in a control system for an internal combustion engine, provided with learning function, and more particularly to the improvements in an air-fuel ratio control system provided with learning function, for the internal combustion engine which is operated in such a manner that a plurality of combustion conditions in each cylinder are changed over from one to another.
2. Description of the Prior Art
Most automotive vehicle engines are equipped with an air-fuel ratio control system for controlling air-fuel ratio of air-fuel mixture to be supplied to the engine at a target value. It has been hitherto proposed to provide learning function to the air-fuel ratio control system, as disclosed in Japanese Patent Provisional Publication No. 5-156994. This air-fuel ratio control system is arranged as follows: Actual air-ratio of air-fuel mixture is judged whether to fall within a rich side or within a lean side relative to a target air-fuel ratio (for example, stoichiometric air-fuel ratio) by comparing an output value of an oxygen sensor disposed in an exhaust system with a slice level (corresponding to the target air-fuel ratio). In accordance with the result of this judgment, an air-fuel ratio feedback correction coefficient .alpha. is set to increase or decrease under proportional-plus-integral control and the like. Then, a basic fuel injection quantity Tp is corrected with the air-fuel ratio feedback correction coefficient .alpha. thereby omitting the deviation of actual air-fuel ratio from the target air-fuel ratio which deviation is owing to error of component parts, deterioration with time lapse, circumferential change and the like. The basic fuel injection quantity Tp is calculated in accordance with an intake air (flow) quantity detected by an airflow meter, and an engine speed of the engine.
The learning function is configured as follows: A deviation of the air-fuel ratio feedback correction coefficient .alpha. from a standard value (a converged target value) is updated and stored as a learning value PHOS in each of a plurality of learning regions (or engine operating regions) in a learning map which leaning regions correspond to the respective engine operating regions or ranges. The basic fuel injection quantity Tp is corrected with the leaning value PHOS thereby approximately coinciding a basic air-fuel ratio (to be obtained without the air-fuel ratio feedback correction coefficient .alpha.) with the target air-fuel ratio. This promotes convergence of actual air-fuel ratio to the target air-fuel ratio in the air-fuel ratio feedback control. In other words, by utilizing the learning function in combination with air-fuel ratio feedback control, correction requirements (for the fuel injection quantity) different depending upon engine operating conditions can be met at a high response so as to effectively control actual air-fuel ratio around the target air-fuel ratio.
Furthermore, another Japanese Patent Application First Publication No. Heisei 5-202816 (published on Aug. 10, 1993) exemplifies a previously proposed control system for performing a learning control over an air-fuel mixture ratio (also called, the air-fuel (A/F) ratio) in the internal combustion engine in which a purge processor for purging an evaporated (vaporized) fuel in a fuel tank into an intake air system of the engine under a predetermined engine driving condition.
In the previously proposed control system, the learning on the air-fuel ratio is carried out independently of an execution or no execution of the purge of the vaporized fuel through the purge processor during a homogeneous charge combustion in the stoichiometric air-fuel mixture ratio control.